IEEE 802.16 is newly developed techniques and protocols as a wireless alternative for cable, DSL services for last mile broadband access. It supports low latency applications such as voice and video, provides broadband connections of both Line-Of-Sight (LOS) and None-LOS (NLOS) between a mobile station (MS) and a base station (BS), and will support hundreds if not thousands of mobile stations from a single BS. With the new features and advantages, it is taken as one of the most promising candidates for future wireless access communication (4G). However, for more widely acceptance by the users, some bottleneck problems have to be solved. One of the key issues is coverage capability. IEEE802.16 works at the spectrum ranging above 2 GHz that is much higher than that of current systems and LOS propagation is preferred. As a result, the coverage is limited, especially in urban areas. At the edge of cells or in shadowed areas, some blind areas can be found due to complex radio environments. In addition, due to the high spectrum, indoor coverage turns to be a key issue and currently there has been no effective solution.
IEEE 802.16 mobile multi-hop relay (MMR) study group was newly founded in July 2005, focusing on extension of IEEE 802.16 for multi-hop and relay. It employs mobile multi-hop relay techniques between base station and mobile station, and thereby specifies a system and function on PHY and MAC layers to support the multi-hop relay. This amendment provides specifications for coverage extension and throughput extension, while being compatible with IEEE Std. 802.16e. The objectives of the relay introduction are throughput enhancement and coverage extension. But currently only throughput enhancement is achieved through simple relaying from contributions. No mature and efficient scheme is available for coverage extension since control signal cannot directly reach the MS when MS is out of the coverage of BS. Technical solution for coverage extension is urgently required in the standardization.
In the IEEE802.16 session #41 (January 2006), the study group has succeeded in defining the PAR (project authorization requirement) for the mobile multi-hop relay. The PAR clearly requires that the introduced relay station (RS) should be completely transparent to the legacy IEEE 802.16e mobile stations, which means that no change is permitted on the current specifications and protocols of IEEE 802.16e mobile station. And the PAR also requires that the complexity of the RS should be significantly less than the complexity of the BS, and the frame definition is OFDMA based. All these description and limitation give a definite description of the IEEE 802.16 RS and show a guideline for the technical solution for coverage extension in the relaying network.